Photoacoustic imaging is known in the literature but it is typically accomplished using a one dimensional array of detectors recording the signal from an optical transducer that generates a single pulse of 5-50 nanosecond duration. The systems that use this process are complicated to use and manufacture. These systems are not readily useful for applications such as cancer detection due to the requirements for the size of the device required to detect this acoustic chirp, and the processing power required to convert the detected signals into an image.
Another method used to generate the signal for the array of detectors to record is using echo based ultrasound, and employing a phased array of transmitter elements. This is where a signal is generated by an array of acoustic transducers and reflected off an object of interest. Echo based ultrasound is currently used in the medical field.
There is a need for a more elegant method to produce photoacoustic images in areas such as detection of cancer in internal organs where small device size is a major benefit. A system where a single lens assembly focuses the acoustic image onto a single 2 dimensional array of transducers would be a significant improvement to the art.
Additionally, major improvements in the art would be to create an acoustic imaging zoom lens, and other lenses capable of imaging acoustic signals that originate from a scene a large number of meters (feet) from the imaging system.
Acoustic systems generally utilize a process to determine the range to target features based upon time of flight of an acoustic wave. If the velocity of the acoustic wave within the medium (e.g., water) is known, and the time delay from pulse launch to receipt can be accurately measured, the distance can be determined. The issue with this approach is that the signal is restricted to a string of pulses that can be clearly identified so that all ambiguity of correlation can be removed. Moreover, spurious reflections, even multiple reflections can generate erroneous range data.
By comparison, an imaging system based upon acoustic lens imaging develops an image in a manner very similar to an optical camera system. This provides very little range information unless parallax is employed. Parallax is what allows humans to rapidly determine the range to the handle of a coffee cup so that hand motion accurately intercepts it. The binocular vision system generates data with angular content from which the range to an object can be accurately determined. This, in fact, is the principle behind coincidence range finders long used aboard tanks and ships to establish the range to target for the main fire control systems. Laser range finders have taken over this function in recent years, but for decades, the coincidence range finder provided accurate range data using parallax. Parallax is a form of triangulation. However in the imaging system described here, the utilization of parallax, or binocular vision, can allow real time stereoscopic acoustic vision within object space with very little computational overhead.
Magnetic resonance scanning, ultrasounds, and soft x-ray scans are 3 tools currently used to detect breast cancers, all of which are limited in their usefulness. Magnetic resonance images are expensive to create. Many general practitioners do not have direct access to these machines nor do they possess the specialized training necessary to interpret the resulting images, so there is an inefficiency in the implementation of MRI systems.
The images produced by normal ultrasound tend to be both coherent and grainy, so specialized training is required for an individual to be able to recognize the features that are produced by the image. As one who is skilled in the art realizes a coherent image is characterized by spatially varying amplitude distortion whereas an incoherent image is characteristic of normal, healthy human vision. If one integrates (averages) the detection of the image over a long enough period of time, then one should be able to create time averaged coherent image which gives the appearance to a detection device of an incoherent image.
X-rays have radiation issues, especially for women in child bearing years.
The present invention overcomes these obstacles.
Without wishing to be bound to any particular theory, applicant believes that the photoacoustic excitation of blood cells by IR radiation absorption causes rapid thermal expansion and an (related) acoustic pulse over several frequencies. The range of frequencies and the intensity of the acoustic pulse are believed to be due to the concentration of hemoglobin in the blood cells, the type of tissue, and the wavelength of photo excitation.
If the initial IR radiation is transmitted to the hemoglobin containing tissue (arteries, veins, capillaries) via a pulse, the resulting acoustic pulse can be identified and, by extension, filtered or gated so one can differentiate signal from the noise. Moreover, a properly designed acoustic lensing arrangement can be so devised as to enable rapid assessment of depth in the imaged scene by using the parallax or similar method.
With higher amounts of energy used to excite the blood cells, it may be possible to get the blood cells to emit waves at a higher frequency spectral band, but this may be damaging to the blood cells and surrounding tissues. If the blood cells emit waves at a higher frequency spectral band, the resulting image will have higher resolution as the resolution diffraction limited cutoff frequency will increase. The range of acoustic frequencies generated currently falls in the 2 MHz to 10 Mhz range.